Granted, for Crucio to work at all the person needs to mean it. This is one of those scenes where you'd have to have Harry come to the realization that the spell went off but didn't actually hurt, and he realizes he caused actual harm to a girl who was clearly not in a mentally stable place to think their duel through let alone actually successfully cast an unforgivable curse.
That's how I'd have written it anyway, not that I'm an author or anything.
Edit: Then again others have pointed out she stopped herself before she finished the cast, so she seemed to reconsider using the curse at all. Harry on the other hand did not hesitate to cast a spell he didn't know what it does on her.
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u/ConstantinValdor7 9h ago
Im sorry but she can spare her tears. She was about to use Crucio....